Search

• Sapphire and Cu can be directly welded through femtosecond laser-induced micro-welding under non-optical contact conditions. • Prefabricated titanium (Ti) film on the sapphire surface via femtosecond laser-induced backward transfer were used to improve the bonding strength. • The interface connection mechanism and reinforcement mechanism of sapphire and purple copper were studied. The ability to weld metals and sapphire is widely required in aerospace, micro-electro-mechanical systems and microwave energy delivery devices. The experiments of femtosecond laser welding between sapphire and copper (Cu) were conducted under non-optical contact conditions. And the effect of pre-fabricating a Ti film on the sapphire surface using femtosecond laser on the bonding strength of ssapphire/Cu joint was investigated. The interface of the sapphire/Cu directly welded by femtosecond laser contains a mixture of sapphire and copper, and the shear strength of the sapphire/Cu interface was approximately 46.4 MPa. The results indicated that the laser-induced molten state of sapphire and the laser-ablated copper mixed together at the interface, filling the gaps and forming an effective metallurgical bond. And then, in the case that the Ti film was prepared on the sapphire surface through femtosecond laser-induced backward transfer (LIBT), a Ti transition layer between sapphire and cooper was observed on the bonding interface of the joint, and the shear strength of the joint increased to approximately 115.5 MPa. A mixture of sapphire, copper, titanium, and titanium oxide was observed at the interface of the joint. The Ti layer between sapphire and copper may effectively alleviated residual stresses at the interface and promoted bonding between copper and sapphire, thereby improving the strength of the joint. The methods and results of this study have reference value for the ultrafast laser bonding between other transparent brittle materials and metals. [ABSTRACT FROM AUTHOR]

As important part of components for 193 nm lithography, AlF 3 coatings deposited by resistive heating method acquire advantages like lower optical loss and higher laser damage threshold, but they also possess some disadvantages like worse stability, which is what aging effect focuses on. AlF 3 single-layer coatings were deposited; optical property, surface morphology and roughness, and composition were characterized in different periods. Owing to aging effect, refractive index and extinction coefficient increased; larger and larger roughness caused more and more scattering loss, which was in the same order with absorption at 193.4 nm and part of optical loss; from composition analysis, proportional substitution of AlF 3 by alumina may account for changes in refractive index as well as absorption. [ABSTRACT FROM AUTHOR]

A doubly Q-switched Nd:GGG laser emitting 1064 nm wavelength with an acousto-optic modulator (AOM) and a monolayer graphene saturable absorber (SA) is presented to study the pulse characteristics. In comparison with singly passive Q-switched laser (SPQSL) with grapheme SA, the doubly Q-switched laser (DQSL) can effectively shorten the pulse width and improve the pulse peak power. The existence of the ramping behavior of pulse characteristics versus modulation frequency in DQSL is shown. The average output power, the pulse width, the pulse energy and the peak power are related to modulation frequency of AOM, and the point of inflection is dominated by pump power. [ABSTRACT FROM AUTHOR]

Based on the dual-loss modulation, i.e. electro-optic (EO) modulator and GaAs saturable absorber, a sub-nanosecond mode-locked pulsed Nd:GGG laser with kHz repetition rates is presented for the first time. The repetition rate (0.5–10 kHz) of this pulsed laser is controlled by the modulation rate of EO modulator, so high stability can be obtained. The sub-nanosecond pulse width depends on the mode-locked pulse underneath the Q-switched envelope in the Q-switched mode-locked (QML) laser and high peak power can be generated. The condition on the generation of sub-nanosecond pulse and the needed threshold power for different modulation rates of EO are given. The average output power, the pulse width and the peak power versus pump power for different repetition rates are demonstrated. The shortest pulse width is 426 ps and the highest peak power reaches 239.4 kW. The experimental results show that the dual-loss modulation technology with EO and GaAs saturable absorber in QML laser is an efficient method to generate sub-nanosecond mode-locked pulsed laser with kHz repetition rates. [ABSTRACT FROM AUTHOR]

• Two types of waveguides are formed by plasma filament arrays. • Plasma waveguides can realize long-distance propagation of terahertz waves. • In the hollow cylindrical plasma waveguide, TE 01 mode experiences lower loss. • The free-space photonic crystal waveguide is better in different aspects. Remotely directional transmission of terahertz (THz) wave in free space is essential in fields of astronomy, space and ground based communications, as well as sensing for atmospheric pollutants, etc. In previous studies, large-aperture halfway mirrors were employed in order to fully collect and then focus the heavily naturally diffracted beam of THz wave to the final target. In this case, however, the broad THz beam not only made a large-size transmission system, but also led to a heavy energy loss due to water vapor absorption within the beam cross-section. Here, we theoretically proposed two index-guiding-based THz waveguide structures composed of plasma filament arrays in air, i.e., hollow cylindrical plasma (HCP) waveguide and free-space photonic crystal (FPC) waveguide (triangular lattice point matrix with a central point defect). Both structures have been demonstrated to well support THz propagation modes, which were confined inside the tiny central air core of the waveguide for an attenuation length up to hundreds of meters. Compared with each other, the FPC waveguide exhibited better performances, including smaller mode field diameter, longer attenuation length and better single-mode property for a broad THz band, making this scheme a promising candidate for long-distance guidance of THz waves in the atmosphere. [ABSTRACT FROM AUTHOR]

Because of its important role both in fundamental theory and applications in quantum information, evolution of entanglement in a quantum system under decoherence has attracted wide attention in recent years. In this paper, we experimentally generate a high-fidelity maximum entangled two-qubit state and present an experimental study of the decoherence properties of entangled pair of qubits at collective (non-collective) bit-flip and phase-shift noises. The results shown that entanglement decreasing depends on the type of the noises (collective or non-collective and bit-flip or phase-shift) and the number of qubits which are subject to the noise. When two qubits are depolarized passing through non-collective noisy channel, the decay rate is larger than that depicted for the collective noise. When two qubits passing through depolarized noisy channel, the decay rate is larger than that depicted for one qubit. [ABSTRACT FROM AUTHOR]

By employing the mixed crystal Nd:Lu 0.5 Y 0.5 VO 4 and the single crystal Nd:YVO 4 as the laser media, the characteristics of the QML laser doubly modulated by electro-optic (EO) modulator and transmission semiconductor saturable absorber (T-SSA) are studied. Under the same cavity parameters, the properties of the low repetition rate sub-nanosecond pulses generated from Nd:Lu 0.5 Y 0.5 VO 4 and Nd:YVO 4 laser are compared. The experimental results show that Nd:Lu 0.5 Y 0.5 VO 4 laser can generate shorter pulse width than Nd:YVO 4 laser, and meanwhile, needs lower pump power to generate low repetition rate sub-nanosecond pulses. The shortest pulse durations obtained from the doubly QML Nd:Lu 0.5 Y 0.5 VO 4 and Nd:YVO 4 lasers are estimated to be 204 and 294 ps, with the corresponding peak power of 3.4 and 3.04 MW, respectively. [ABSTRACT FROM AUTHOR]

Lateral-pin germanium silicon avalanche photodiodes (APDs) offer great potential for improving performance, cost-effectiveness, and versatile production processes for large-capacity data communication applications. However, excessive avalanche multiplication noise limits the increase in bandwidth. In this study, we propose and design the integrated peaking inductors to enhance the bandwidth of a lateral pin Ge/Si APD without compromising the direct current (DC) characteristics. By introducing the spiral inductor to counteract the capacitive effect of APD, the RF output power at high frequency can be effectively increased, thus improving the photodiode bandwidth. The impact of different sizes of inductors and APDs on the performance was experimentally investigated. The resulting APDs, with Ge lengths of 20 μ m (Ge20) and 45 μ m (Ge45), provided low dark currents of 11 nA and 27 nA, and primary responsivities of 0.85 A/W and 1.05 A/W at −1 V, respectively. A small inductor (375 pH) exhibited greater bandwidth enhancement than a large inductor (622 pH) and the Ge20 APD achieved a bandwidth of up to 78 GHz. For the larger Ge45 APD, the bandwidth was maintained above 50 GHz, even close to the breakdown voltage, and a high gain-bandwidth product of up to 609 GHz was calculated by an avalanche multiplication gain of 11.7. This result may provide ideas for balancing the speed and sensitivity of lateral-pin APDs used in high-speed optical communications. • We demonstrate an avalanche photodiode using the inductive gain peaking technique. • An equivalent circuit model is used to simulate the bandwidth of the proposed APD. • The bandwidth of 78 GHz and gain-bandwidth-product of 609 GHz are obtained. • It provides a new way to balance the speed and sensitivity of APDs. [ABSTRACT FROM AUTHOR]

• 2D MoTe 2 nanosheets were fabricated and characterized. • A sub-nanosecond IOPO pumped by a hybrid Q-switched laser has been realized. • Simulation results agreed with the experimental results well. In this paper, few-layered molybdenum ditelluride (MoTe 2) nanosheets are synthesized with a liquid-phase exfoliation method. Its appearance, the spectra and the saturated absorption characteristics are measured. By using MoTe 2 as saturable absorber (SA), a passively Q-switched YVO 4 /Nd:YVO 4 laser is realized. At an incident pump power of 6.64 W, a maximum output power of 1.14 W with a minimum pulse duration of 66.2 ns is obtained. To our knowledge, this is the shortest pulse width ever achieved from a passively Q-switched laser with a MoTe 2 -SA at 1.06 μm. Based on this, a sub-nanosecond KTiOPO 4 (KTP) based intracavity optical parametric oscillation (IOPO) pumped by a hybrid Q-switched laser with a MoTe 2 -SA and an acousto-optic modulator (AOM) is realized. At an incident pump power of 10.4 W and an AOM repetition rate of 10 kHz, a maximum output power of 195 mW with a minimum pulse duration of 835 ps for signal wave is obtained. To solve the IOPO rate equations, the ground-state and excited-state absorption cross sections of MoTe 2 are rationally calculated to be 1.32 × 10−18 cm2 and 9.15 × 10−19 cm2 according to the observed transmittance curve, respectively, and the excited-state lifetime is 376.2 µs. The numerical solution of the equations matches well with the experimental data. [ABSTRACT FROM AUTHOR]

• MoTe 2 nanoflakes were successfully exfoliated by liquid phase exfoliation. • The saturable absorption property of the film at ~3 μm was characterized. • Q-switched laser at ~3 μm based on the MoTe 2 film was realized. • 2 dimensional MoTe 2 film is an outstanding passive modulator at ~3 μm. The stable nano-seconds pulsed Er:Lu 2 O 3 laser were realized by employing a molybdenum ditelluride (MoTe 2) saturable absorber (SA), which was fabricated with the liquid phase exfoliation (LPEx) method. Under the absorbed power of 7.24 W, the maximum average output power of 0.52 W was achieved in a repetition rate of 105 kHz and a pulse duration of 317 ns at 2.85 μm, corresponding to a pulse energy of 4.94 μJ and a peak power of 15.6 W. [ABSTRACT FROM AUTHOR]

In this paper, a sub-nanosecond KTiOPO 4 (KTP)-based intracavity optical parametric oscillator (IOPO) pumped by a dual-loss modulated Q-switched and mode-locked (QML) laser with an acousto-optic modulator (AOM) and a Cr 4+ :YAG saturable absorber (Cr 4+ :YAG-SA) has been demonstrated. By changing the initial transmission of Cr 4+ :YAG-SA and the transmission of the output coupler at the signal wavelength, the signal pulse width compression can be realized. At an incident pump power of 8.3 W and an AOM repetition rate of 15 kHz, a single signal pulse underneath Q-switched envelope with the shortest pulse width of 220 ps was obtained. The experimental results reveal that this is a simple and effective way to obtain the sub-nanosecond OPO signal pulses. In addition, the related coupled rate equations have been set up and the simulation results agreed with the experimental results well. [ABSTRACT FROM AUTHOR]

An intracavity KTiOPO 4 (KTP) optical parametric oscillator (OPO) pumped by a Kerr lens mode-locking (KLM) Nd:GGG laser near 1062 nm with a single AO modulator was realized for the first time. The mode-locking pulses of the signal wave were obtained with a short duration of subnanosecond and a repetition rate of several kilohertz (kHz). Under a diode pump power of 8.25 W, a maximum output power of 104 mW at signal wavelength near 1569 nm was obtained at a repetition rate of 2 kHz. The highest pulse energy and peak power were estimated to be 80 μJ and 102 kW at a repetition rate of 1 kHz, respectively. The shortest pulse duration was measured to be 749 ps. By considering the Gaussian spatial distribution of the photon density and the Kerr-lens effect in the gain medium, a set of the coupled rate equations for QML intracavity optical parametric oscillator are given and the numerical simulations are basically fitted with the experimental results. [ABSTRACT FROM AUTHOR]

We report a passively continuous-wave mode-locked (CWML) Nd:Gd 0.19 Y 0.81 VO 4 laser oscillating at 1342.3 nm for the first time in this paper. Stable mode-locked pulse cluster with a pulse width of 7.2 ps and a pulse repetition frequency of 32.8 MHz has been realized with a semiconductor saturable absorber mirror (SESAM). The highest output power was 880 mW when the incident pump power was 7.1 W, corresponding to an optical conversion efficiency of 12.4%. The mode-locked pulse energy was about 26.83 nJ, while the peak power was 3.73 kW. [ABSTRACT FROM AUTHOR]

Abstract: A diode-end-pumped passively Q-switched ytterbium-doped yttrium aluminum garnet (Yb:YAG) laser with gallium arsenide (GaAs) wafer as saturable absorber has been realized. In the experiment, two pieces of GaAs wafers with respective thicknesses of 400 and 700 μm were used respectively. The output laser characteristics such as the pulse duration, single pulse energy and peak power, have been measured. By using thicker GaAs wafer as saturable absorber, a minimum pulse duration of 3.5ns was obtained with an average output power of 361mW and a pulse repetition rate (PRR) of 25kHz, corresponding to a single pulse energy of 19.6μJ and a peak power of 5.7kW. With a 400μm-thick GaAs wafer as saturable absorber, a maximum output power of 469 mW was achieved. The central wavelength of the laser was measured to be 1050.4nm at pump power of 7.8W and dual wavelength operation peaked at 1049.3nm and 1051.6nm was observed at a high pump power of 10W. By considering Gaussian spatial distribution and the thermal effects in the gain medium, the coupled rate equations for passively Q-switched Yb:YAG laser with GaAs saturable absorber were given. [Copyright &y& Elsevier]

Abstract: In this paper, by considering Gaussian distribution of the intracavity photon density, the coupled rate equations for the diode-pumped doubly Q-switched and mode-locked (QML) laser with EO modulator and GaAs saturable absorber are presented. These equations are numerically solved, and the key parameters of an optimally coupled doubly QML laser have been determined. These key parameters include parameters of the gain medium, the small-signal transmission of saturable absorber as well as the modulation frequency of EO modulator, which can maximize the pulse energy of singly Q-switched envelope. A diode-pumped doubly QML Nd:Lu0.15Y0.85VO4 laser with EO modulator and GaAs saturable absorber is constructed, the experimental results have verified numerical simulation applicable. [Copyright &y& Elsevier]

• SnTe quantum dots (QDs) were prepared by the UALPE method. • A SnTe QDs SA based mode-locked YDFL with pulse width of 265 ps was obtained. • This work demonstrated that SnTe is a promising saturable absorber. Tin telluride (SnTe), a member of group IV-VI semiconductors, has attracted significant attention due to its super thermoelectricity and ferroelectricity. In addition, SnTe was reported to have a direct bandgap (0.18 eV) and relatively good oxidation resistance, therefore, it has huge application potential in optoelectronics. However, up to now, the study of interaction between light and SnTe is still immature. In this paper, SnTe quantum dots (QDs) were prepared by the ultrasonication assisted liquid-phase exfoliation (UALPE) method and the broadband absorption properties of SnTe QDs were demonstrated. Furthermore, by employing SnTe QDs as a saturable absorber (SA), a stable mode-locked Yb-doped fiber laser (YDFL) with a pulse duration of 265 ps and an output power of 5.68 mW was obtained. Our results demonstrated that SnTe could be a promising candidate in the mode-locked YDFL system and photonic technology application. [ABSTRACT FROM AUTHOR]

• Two-dimensional MXene Ti 3 C 2 T x was fabricated. • A doubly Q-switched Tm:LuAG laser was realized with MXene Ti 3 C 2 T x and AOM. • The narrowest pulse width was 178 ns and highest peak power was 1062 W. MXene Ti 3 C 2 T x (T = F, O, or OH) was fabricated by aqueous acid etching and liquid phase exfoliation method. Its appearance, the spectra and the saturated absorption characteristics were measured. By using MXene Ti 3 C 2 T x as saturable absorber (SA) and an acousto-optic modulator (AOM), a doubly Q-switched Tm:LuAG laser at 2 μm waveband was realized. Under the incident pump power of 9.5 W at modulated repetition rate 1 kHz of AOM, the narrowest laser pulse width of 178 ns was obtained, corresponding to the highest pulse peak power of 1062 W. To our knowledge, this is the shortest pulse width and highest peak power obtained in the Q-switched lasers with MXene Ti 3 C 2 T x as SA. In comparison to the singly Q-switched laser with only MXene Ti 3 C 2 T x or AOM, the doubly Q-switched laser can generate shorter pulse width and higher peak power. The maximum compression ratio of pulse width 6.0 and the highest enhancement factor of peak power 205 were achieved. The experimental results show that MXene Ti 3 C 2 T x is an excellent SA in 2 μm waveband laser system and the doubly Q-switched laser can compress pulse width and improve pulse peak power. [ABSTRACT FROM AUTHOR]